If a woman talks to the owner of the clothes shop only as much as is necessary, with no fitnah involved, there is nothing wrong with it. Women used to talk to men with regard to their needs or matters in which there is no fitnah, within the limits of necessity.
But if it is accompanied by laughter, chatting or softening of the voice, then it is haraam and is not permissible.
Allaah said to the wives of His Prophet (peace and blessings of Allaah be upon him) (may Allaah be pleased with them):
“then be not soft in speech, lest he in whose heart is a disease (of hypocrisy, or evil desire for adultery) should be moved with desire, but speak in an honourable manner”
[al-Ahzaab 33:32 – interpretation of the meaning].
An honourable manner is that which is customarily known as such and is done according to necessity. As for anything more than that, if it is done with laughter and chatting, or with an alluring voice and so on, or she uncovers her face in front of him or uncovers her forearm or hands, all of these actions are haraam and evil, and are causes of fitnah and immorality.
The Muslim woman who fears Allaah must do her duty towards Allaah, and not speak to non-mahram men in ways that may raise their hopes or tempt them. If she needs to go to a shop or a place where there are men, she should be modest and cover herself, and follow Islamic etiquette. If she speaks to men, she should speak in an honourable manner in which there is no fitnah and nothing dubious. End quote.
Fataawa al-Mar’ah al-Muslimah (2/576, 577), edited by Ashraf ibn ‘Abd al-Maqsood.